Matrix transfer mediums are now an established, commercial technology, but as print mechanisms change, existing transfer mediums may not be satisfactory. Typewriters and printers may require a low-friction outer substrate surface to facilitate feeding of the ribbon. Desirable and economic low friction surfaces may be polyolefins and polyesters, particularly polyethylene terephthalate.
Where such a surface is to be the substrate, a matrix formulation must be found to provide good print quality and stability under impact at reasonable cost. Such a formulation has been developed in accordance with this invention employing aliphatic polyurethane.
Polyurethane as the resin in a matrix transfer medium is an established alternative. Typically polyurethane is mentioned only generally in the prior art. U.S. Pat. Nos. 3,037,879 to Newman et al and 3,681,186 to Findlay et al are illustrative of such prior art. Neither mention a specific polyurethane for use, but do list polyurethane as a suitable material. U.S. Pat. No. 3,348,651 to Mater et al does teach the use of a specific urethane. That urethane is Estane polyurethane, an aromatic urethane. The only commercially sold polyurethane binder matrix ribbon known is believed from analysis to be an aromatic polyurethane.
The preferred embodiment of this invention includes a minor amount of a porous magnesium silicate filler. U.S. Pat. No. 3,413,184 to Findlay et al teaches talc as such a filler, as well as pigments and an oily ink vehicle as are conventional in this technology. Talc is naturally occurring magnesium silicate and is not porous. Significant novelty of this invention is believed to be in the aliphatic polyurethane and in the specific overall choice of materials. Significant novelty is also believed to be in the use of porous magnesium silicate as a filler.